1. Field of the Invention
The invention relates to a rotary magnetic head device which is used in a recording/reproduction apparatus such as a VTR.
2. Description of the Background
FIG. 1 is a section view of a rotary magnetic head device which is a first prior art device disclosed in, for example, Japanese Patent Application Laid-Open No. 61-55173 (1986). In the figure, 101 is a stationary cylinder having an outer face on which a guide groove (lead) for guiding a magnetic tape is formed, 102 is a shaft-integrated bearing, 102a is a bearing portion which is pressingly inserted into and fixed to the stationary cylinder 101, and 102b is a rotating shaft which is pressingly inserted into and fixed to a rotary cylinder 103 and rotatable in any direction with respect to the stationary cylinder 101.
The reference numeral 105 is a cylindrical bobbin which is concentric with the rotating shaft 102b. As shown in FIG. 2, step portions 105a and 105b are formed at the both ends of the bobbin in the direction of the rotating shaft 102b, respectively. The reference numeral 171 is a coil which is wound on and fixedly attached to the outer face of the bobbin 105. The reference numeral 181 is a first plate spring which is fixed at an outer periphery portion to the rotary cylinder 103, and welded at an inner periphery portion to the step portion 105a of the bobbin 105. The inner periphery portion is swingable in the direction perpendicular to the sheet in FIG. 2, with respect to the outer periphery portion. The reference numeral 191 is a second plate spring which is fixed at an outer periphery portion to the rotary cylinder 103, and welded at an inner periphery portion to the step portion of 105b of the bobbin 105. Magnetic heads 104a and 104b are fixedly attached to front ends of plate portions which are elongated from the inner periphery portions in the directions of the respective outer peripheries of the second spring plate 191, so as to oppose each other by an angle of 180 deg. The inner periphery portions are swingable in the direction perpendicular to the sheet in FIG. 2, with respect to the outer periphery portions, and also the magnetic heads 104a and 104b are swingable integrally with rite respective inner periphery portions. The reference numeral 110 is a cylindrical back yoke which is fixedly attached to the rotary cylinder 103, and 111 is a cylindrical magnet which is fixedly attached to the inner periphery of the back yoke 110 and is magnetized in the radial direction. The magnet 111 is located so that its inner face opposes the coil 171 and is separated therefrom by about 0.1 mm. The magnet 111 generates magnetic fluxes which perpendicularly intersect with the coil 171 in the space between the inner periphery face and the rotating shaft 102b.
The reference numeral 112 is a first base plate which is fixed to the inside of the rotary cylinder 103 and to which ends of the coil 171 are connected, and 113 is a second base plate which is fixed to the upper end face side of the rotary cylinder 103 and connected to the first base plate 112 through pins 114. The reference numeral 115 is a slip ring having two electrodes fixed to the upper end portion of the rotary cylinder 103. The electrodes are connected to the coil 171 through lead wires 115a, the second base plate 113, the pins 114, and the first base plate 112. The reference numeral 116 is a brush which pressingly contacts with the outer face of the slip ring 115 to externally supply the electric power, 117 is a rotor of a motor which rotor is pressingly fitted onto the rotating shaft 102b, 118 is a stator of the motor which stator is attached to the stationary cylinder 101, 119 is a rotary yoke which is fixed to the rotating shaft 102b at a position opposite to the rotor 117 of the motor, 120 is a rotational rotary transformer attached to the rotary cylinder 103, and 121 is a fixed rotary transformer which is attached to the stationary cylinder 101 at a position opposite to the rotational rotary transformer 120.
First, the operation of recording or reproducing signals on or from a magnetic tape in the thus configured prior art rotary magnetic head device will be described. As shown in FIG. 7, a magnetic tape 100 runs on the rotary cylinder 103 while being wound by an angle (.alpha. in the figure) of 180 deg. or less. The rotary cylinder 103, and the magnetic heads 104a and 104b are rotated, and signals sent from a recording amplifier (not shown) are transmitted in a noncontacting manner through the fixed rotary transformer 121 and the rotational rotary transformer 120 shown in FIG. 1, to the magnetic heads 104a and 104b, thereby obliquely recording the signals on the magnetic tape 100. The magnetic heads 104a and 104b trace signals recorded on the magnetic tape 100, and transmit through the rotational rotary transformer 120 and the fixed rotary transformer 121 to a reproduction amplifier (not shown), thereby reproducing the signals recorded on the magnetic tape 100.
Next, the reproduction conducted on a magnetic tape 100 where there exists a track curve in recording tracks will be described. The linearity of a track recorded on a magnetic tape depends on the machining accuracy of the guide groove (lead) formed on the outer face of the stationary cylinder 101. The machining accuracy of the guide groove (lead) is 2 3 (.mu.m) at the highest. In a case where the magnetic heads 104a and 104b are fixed Lo the rotary cylinder 103 in a system having a track pitch of about 10 (.mu.m) , therefore, the track deviation is caused and the reproduction output is lowered. As a counter measure, means for moving the magnetic heads to follow the curved track is adopted.
In the first prior art rotary magnetic head device having such a configuration, when a current is supplied from the brush 116 through the slip ring 115 to the coil 171, an electromagnetic force according to Fleming's left-hand rule is generated in the coil 171 so that the bobbin 105 is displaced to a position at which the electromagnetic force balances with the resilient forces of the first and second plate springs 181 and 191. This causes the magnetic heads 104a and 104b fixedly attached to the front ends of the plate portion of the second plate spring 191, to displace together with the bobbin. Therefore, an error signal due to a deviation or the magnetic head trace locus from the recording track is detected during the reproduction process, so that the magnetic heads 104a and 104b are moved in accordance with a control signal based on the error signal, thereby enabling the magnetic heads 104a and 104b to follow the curved track,
FIG. 3 shows a rotary magnetic head device which is a second prior art device disclosed in Japanese Patent Application Laid-Open No. 61-55173 (1986). In the figure, 201 is a stationary cylinder which has a lead for adequately holding a magnetic tape 100 while slanting it, and a sleeve at the center, 203 is a rotating shaft which is driven by a motor (not shown) and disposed on the inner face of the sleeve of the stationary cylinder 201, 204 is a holding member fixedly attached to the rotating shaft 203, and 205 is a center pole which is fixedly attached to the holding member 204 and made of a magnetic material. The reference numeral 206 is a rotary cylinder which is fixedly attached to the center pole 205 and rotatable in any direction, 207 is a permanent magnet fixedly attached to the center pole 205, 208 is a yoke which is fixedly attached to the permanent magnet 207 and made of a magnetic material, 209 is a spring attach member attached to the yoke 208, 210 is a plate spring member attached to the spring attach member 209, and 211 is a bobbin which is held by the plate spring member 210 and made of a nonmagnetic material. The reference numeral 212 is a coil which is formed by an insulated wire wound on the outer face of the bobbin 211, 213 is a magnetic head supporting base plate which has a disk-like shape and is attached to the bobbin 211, 214 designates magnetic heads which are attached to the vicinity of the outer face of the magnetic head supporting base plate 213 so as to protrude from the rotary cylinder 206 by a given distance, and 215 is a slip ring connected to the coil 212.
FIG. 4 shows the main portions of a conventional magnetic recording/reproduction apparatus. In the figure, 216 is a deck base, and 217 is a rotary magnetic head device which is fixedly attached to the deck base 216 with a given angle. The reference numeral 218 is an inlet tape guide roller having a flange for regulating the vertical position (the position along the width) of the magnetic tape 100 which is to be wound on the rotary magnetic head device 217. The reference numeral 219 is an inlet slant guide adjacent to the inlet tape guide roller 218 and for slanting the magnetic tape 100 which is to be wound on the rotary magnetic head device 217. The reference numeral 220 is an outlet slant guide for returning the magnetic tape 100 which has been peeled from the rotary magnetic head device 217, to the original state. The reference numeral 221 is an outlet tape guide roller having a flange for regulating the vertical position (the position along the width) of the magnetic tape 100 which has been peeled from the rotary magnetic head device 217. The reference numeral 222 is a tape cassette which is to be placed on the deck base 216 and accommodates the magnetic tape 100.
First, the operation of recording signals on a magnetic tape or reproducing signals from a magnetic tape having a track curve of a small degree in the second prior art rotary magnetic head device having such a configuration will be described. As shown in FIG. 4, the magnetic tape 100 runs while being slanted with respect to the rotary magnetic head device 217 with a given angle and wound on the outer face of the device 217, the rotary cylinder 206 and the magnetic heads 214 are rotated by driving the motor, and signals sent from a recording circuit (not shown) are transmitted in a noncontacting manner through rotary transformers (not shown) to the magnetic heads 214, thereby obliquely recording the signals on the magnetic tape 100. The magnetic heads 214 rotated by driving the motor trace signals recorded on the magnetic tape 100, and transmit in a noncontacting manner through the rotary transformers to a reproduction circuit, thereby reproducing the signals.
Next, the reproduction conducted on a magnetic tape 100 where there exists a track curve will be described. In a case where a magnetic tape having a track curve as shown in FIG. 5 is to be subjected to the reproduction process using a rotary magnetic head device in which the magnetic heads 214 are fixed, it is impossible to accurately trace the tracks, thereby producing portions of a reduced reproduction output level. Accordingly, a current is supplied through the slip ring 215 from a brush (not shown) connected external to the coil 212, whereby an electromagnetic force is generated so that the bobbin 211 moves in the axial direction of the rotating shaft 203 to a position at which the electromagnetic .force balances with the resilient force of the plate spring member 210. This causes the magnetic heads 214 attached to the front, end of the magnetic head supporting base plate 213 fixedly attached to the bobbin 211, to move in the axial direction of the rotating shaft 203. In the reproduction process, therefore, the relative positional relationship between the recording track and the magnetic heads 214 is detected, and a current of an adequate level is supplied through the slip ring 215 of the rotary magnetic head device 217, thereby moving the magnetic heads 214 so as to accurately follow the curved recording track as shown in FIG. 6.
Since a prior art rotary magnetic head device is constructed as described above, two magnetic heads cannot operate independently from each other. For example, in a case where the first prior art rotary magnetic head device is applied to a system in which the wrap angle of the magnetic tape 100 is 180 deg. or less as shown in FIG. 7, it is not necessary for the two magnetic heads 104a and 104b to simultaneously follow a track on the magnetic tape 100. Therefore, the two magnetic heads 104a and 104b are not required to operate independently from each other. By contrast, in a case where such a device is applied to a system in which the wrap angle of the magnetic tape 100 is greater than 180 deg. as shown in FIG. 8, there is a period during which the two magnetic heads 104a and 104b simultaneously contact with the magnetic tape 100. When the magnetic head 104a Follows a track on the magnetic tape 100, therefore, the magnetic head 104b must follow another track on the magnetic tape 100, thereby producing a problem in that such a prior art rotary magnetic lead device cannot be applied to a system in which the wrap angle of the magnetic tape 100 is greater than 180 deg.
Also in the second prior art, rotary magnetic head device, when a plurality of magnetic heads 214 are used, all the magnetic heads are simultaneously moved. For example, n a case where two magnetic heads 214a and 214b are provided as shown in FIGS. 9 and 10, when the wrap angle of the magnetic tape 100 on the rotary magnetic head device 217 is less than 180 deg., even a prior art device such as shown in FIG. 3 can cope with a track curve. When the wrap angle exceeds 180 deg., however, in a certain portion of the period when the magnetic head 214a contacts with the magnetic tape 100, the magnetic head 214b also contacts with the magnetic tape 100. As a result, the operation of moving the magnetic head 214a so as to follow a track causes the magnetic head 214b to move in the same manner as the magnetic head 214a, resulting in that, when a magnetic tape 100 having a track curve is to be subjected to the reproduction process, the magnetic head 214b cannot follow a curved recording track. This produces a problem in that the signal output from the magnetic head 214b is lowered in level.
A rotary magnetic head device which can solve such a problem has been proposed. FIGS. 11 and 12 show a rotary magnetic head device which is a third prior art device disclosed in Japanese Patent Application Publication No. 5-8486 (1993). FIG. 11 is a section view showing the prior art rotary magnetic head device for dynamic head tracking, and FIG. 12 is an exploded perspective view of the device of FIG. 11. In FIG. 11, 301 is a stationary cylinder for guiding on its outer face the magnetic tape 100 which is a recording medium, 302 designates two bearings which are respectively fixed at their outer ring to two bearing-supporting projections 230 and 231 formed on the stationary cylinder 301, 303 is a rotating shaft which is supported by the bearings 302 so as to be rotatable with respect to the stationary cylinder 30l, and 304 is a rotary cylinder which is integrally fixed to the rotating shaft 303. The reference numeral 305 is a primary side of a ring-like rotary transformer which is coaxial with the rotating shaft 303 and fixed in a plane perpendicular to the rotating shaft, and 306 is a secondary side of the rotary transformer which is separated from the primary side 305 by a small gap so as to oppose it and is fixed to the rotary cylinder 304. The reference numeral 307 is a first annular plate spring which is attached to the rotary cylinder 304 by first and second fixing portions 308 and 309 separated from each other by an angle of 180 deg., so that the plate spring forms a plane perpendicular to the rotating shaft 303.
The reference numerals 310 and 311 are first and second posts for attaching the first plate spring 307 to the rotary cylinder 304, 312 is a first arcuate holder having one end fixed to a portion of the First plate spring 307 which portion is separated from the first fixing portion 308 by an angle of 90 deg., and 313 is a second arcuate holder having one end fixed to another portion of the first plate spring 307 which portion is separated from the second fixing portion 309 by an angle of 90 deg, The reference numeral 314 is a first sectorial magnet A which is disposed in the first holder 312 so that the inner periphery side positioned in the rotary cylinder 304 is the N-pole, and 315 is a second sectorial magnet A which is disposed in the first holder 312 so that the inner periphery side positioned in the rotary cylinder 304 is the S-pole. The reference numeral 316 is a first magnet B which is disposed in the second holder 313 so that it opposes the first magnet A 314 by an angle of 180 deg, about the rotating shaft 303, and that the inner periphery side is the N-pole, and 317 is a second magnet B which is disposed in the second holder 313 so that it opposes the second magnet A 316 by an angle of 180 deg. about the rotating shaft 303, and that the inner periphery side is the N-pole. The reference numeral 318 is a first head base having one end fixed to the first holder 312, and the other end protruding in the vicinity of the outer face of the stationary cylinder 301, and 319 is a first magnetic head which is attached to a portion of the first head base 318 in the vicinity of the outer face of the stationary cylinder 301, and has a front end protruding the stationary cylinder.
The reference numeral 320 is a second head base having one end fixed to the second holder 313, and the other end protruding in the vicinity of the outer face of the stationary cylinder 301, and 321 is a second magnetic head which is attached to a portion of the second head base 320 in the vicinity of the outer face of the stationary cylinder 301, and has a front end protruding the stationary cylinder 301. The reference numeral 322 is a second annular plate spring which is fixed to the other ends of the first and second holders 312 and 313, and at portions 323 and 324 to the first and second posts 310 and 311 by screws 325 and 326. The reference numeral 327 is a cylindrical base which is fixed at one end to the stationary cylinder 301 and coaxial with the rotating shaft 303, 328 is a first coil which is attached to the base 327 so as to oppose the first magnet A 314 and the first magnet B 316, 329 is a second coil which is attached to the base 327 so as to oppose the second magnet A 315 and the second magnet B 317, 200a is a head moving unit, and 300 is the rotary magnetic head device.
Next, the operation of the prior art device will be described. Regarding the first magnetic head 319, when a driving current is supplied to the first and second coils 328 and 329 intersecting with the magnetic field in the magnetic circuit formed by the first and second magnets A 314 and 315, a driving force is generated in the axial direction. This driving force causes the first magnetic head 319 which is integrally attached to the first holder 312 of the moving unit, to move in the axial direction. This is applicable also to the second magnetic head 321. Since the magnetization direction of the second magnet A 315 is contrary to that of the second magnet B 317, however, the first and second holders 312 and 313 are moved in the directions opposite to each other, respectively. In other words, the first and second holders 312 and 313 can be moved independently from each other by controlling the level and direction of the driving currents supplied to the first and second holders 312 and 313.
TABLE 1 ______________________________________ 1 st Holder 2 nd Holder ______________________________________ Current Direction 1 st Coil: (+) 0 2 F 2 nd Coil: (+) 1 st Coil: (+) 2 F 0 2 nd Coil: (-) 1 st Coil: (-) -2 F 0 2 nd Coil: (+) 1 st Coil: (-) 0 -2 F 2 nd Coil: (-) ______________________________________
In order to describe the driving method more specifically, the relationship between the directions of currents supplied to the coils and the driving forces generated in the holders will be described with reference to Table 1.
In Table 1, the driving forces respectively applied to the first magnet A 314 and the first magnet B 316 when a driving current A flows through the first coil 328 in the positive direction are F, and the driving forces respectively applied to the second magnet A 315 and the second magnet B 317 when a driving current A flows through the second coil 329 in the positive direction are -F and F. By setting the driving currents of the first and second coils 328 and 329 so as to be equal in level but opposite in direction to each other, it is possible to perform a control in which the first holder 312 is moved and the second holder 313 is not moved. In contrast, by setting the driving currents of the first and second coils 328 and 329 so as to be identical in direction to each other, it is possible to perform a control in which the second holder 313 is moved and the first holder 312 is not moved.
Generally, when approximated with a primary spring or mass system, the control band f which is an important property of such a head moving device can be expressed by Equation 1: EQU f=(1/2.pi.).times.(K/M).sup.1/2 ( 1)
where M is a moving mass, and K is a spring constant of the moving mechanism.
From Equation 1, it will be noted that the track following property of a magnetic head with respect to a recording track can be improved by increasing the spring constant K or decreasing the mass M.
A driving force F required for moving the head moving device is expressed by Equation 2 below: EQU F=K.times.X (2)
where X is a moving distance.
From the above, it will be noted that, in order to move the head moving device by a small driving force, the spring constant K is decreased or the moving range X is reduced.
As seen from the above description, a head moving device having a wide control band f and requiring a reduced driving force can be realized by decreasing the mass M, the spring constant K, and the moving distance X, and increasing K/M. From Equation 2, the case shown in Table 1 where a driving force of 2F is obtained by using two coils and two magnets is equivalent to a case where the spring constant is apparently 2K. From Equation 1, it is expected that the band is widened by about 1.4 times. This is equivalent to an effect which is obtained by reducing the moving mass to half. Since expensive magnets of a high saturation magnetic flux density are generally used, the reduction of the mass is most effective.
Next, a fourth prior art rotary magnetic head device in which the mass is reduced will be described. FIG. 13 is a section view of a rotary magnetic head device which is disclosed in Japanese Patent Application Laid-Open No. 2-304711 (1990). In the figure, 330 is a first yoke having a fitting hole 331, 332 is a first column-like magnet which is attached to the first yoke 330 and in which the first yoke 330 side is the S-pole, 333 is a second column-like yoke which is attached so as to be coaxial with the first magnet 332, and 334 is a second column-like magnet which is attached to the second yoke so as to be coaxial with first magnet 332 and in which the second yoke 333 side is the N-pole. The reference numeral 335 is a first annular plate spring having an outer periphery which is positioned by the first yoke 330, an end to which the magnetic head 319 (321) is attached, and an inner periphery portion which is coaxial with the first magnet 332. The reference numeral 336 is a cylindrical bobbin which is attached at one end to an inner periphery portion of the first plate spring 335 and coaxial with, the first magnet 332, 337 is a coil attached to the bobbin 336, 338 is a second annular plate spring having an inner periphery portion which is attached to the other end of the bobbin 336, and 339 is a third cylindrical yoke which is coaxial with the first magnet 332 and has an end cooperating with the first yoke 330 so as to position and fit the first plate spring 335. The reference numeral 340 is a fourth disk-like yoke having an outer periphery portion cooperating with the third yoke 339 so as to position and fit the second plate spring 338, and an inner periphery portion for fixing the second magnet 334, 341 is a Hall element disposed at the inside of the fourth yoke 340, and 200 is a head moving device consisting of these elements.
The operation of the fourth prior arc example will be described. Principally, this example operates in the same manner as the third prior art example of FIGS. 11 and 12. The fourth prior art example is of the electromagnetic drive type, but differs from the third prior art example in that only a single coil, i.e., the coil 337 is used and the moving portion is not the magnet portion but the coil portion. Since two magnets are used so as to sandwich the second yoke 333, the size of a magnet it circuit in a magnetic head moving direction 342 can be increased, thereby increasing the moving distance of the magnetic head 319 (321) moving integrally with the bobbin 336 which is integral with the coil 337. Generally, the head moving device 200 is used while being incorporated into a rotary magnetic head device.
FIG. 14 is a section view showing the main portions of the rotary magnetic head device 300 to which the head moving device 200 is attached, and FIG. 15 is a plan view showing the main portions of the rotary cylinder 304 to which the head moving device 200 is attached. In the figures, 343 is a hole formed in the rotary cylinder 304 so that the head moving device 200 is attached to the rotary cylinder 304 by screws 344, 345 is a flange to which the rotary cylinder 304 is attached by screws 346 and which is integral with the rotating shaft 303, 347 is a driving transfer base plate for the head moving device 200 and fixed to the rotary cylinder 304, 348 is an external brush which slidingly connects the driving transfer base plate 347 with the external of the rotary magnetic head device 300, and 349 is a slip ring disposed in the side of the rotary cylinder 304.
In the figure, a power is externally supplied to the driving transfer base plate 347 through the sliding contact between the brush 348 and the slip ring 349, so that a driving current is supplied from the driving transfer base plate 347 to the coil 337 of the lead moving device 200. The coil 337 is formed so as to intersect a first magnetic circuit consisting of the first magnet 332, and the first to third yokes 330, 333 and 339, and a second magnetic circuit consisting of the second magnet 334, and the second to fourth yokes 333, 339 and 340. When a driving current is supplied to the coil 337, the bobbin 336 to which the coil 337 is attached moves in the magnetic head moving direction 342. Since the magnetic force generated by the coil 337 in the magnetic lead moving direction 342 is proportional to the moving distance of the bobbin 336 due to the driving current, the moving distance of the bobbin 336, namely the moving distance of the magnetic head 319 (321) can be substantially detected in the term of the output of the Hall element 341.
The third prior art device having the configuration described above has problems such as that, in order to increase the width of a control band shown by Equation 1 for the independent driving of the magnetic heads, two moving magnets are required for each of the magnetic leads, thereby increasing the production cost, and that, when a plurality of magnetic heads are to be :independently driven at the same time, a complex control circuit for conjointly controlling two coils is required. By contrast, in the fourth prior art device having the configuration described above, the moving unit, which is problematic it, the third prior art device, can be lightened so that the control band is broadened. However, in the fourth prior art device, a sliding contact unit, realized by, for example, a combination of a slip ring and a brush thereby producing a problem in that it is difficult to ensure the life and the reliability due to the service environment.
The procedure of assembling the third prior art device will be described. The assembling procedure requires complex steps as follows: In FIGS. 11 and 12, the head moving unit 200a which consists of the first and second plate springs 307 and 322, the first and second holders 312 and 313, etc. is attached to the rotary cylinder 304 by the screws 325 and 326. Then, the secondary rotary transformer 306 is fixed to the rotary cylinder 304 while sandwiching the base 327 to which the first and second coils 328 and 329 are fixedly attached. Thereafter, the rotary cylinder 304 is inserted toward the stationary cylinder 301. In this way, the base 327 to which the first and second coils 328 and 329 are fixedly attached, and the secondary rotary transformer 306 are assembled in such a manner that they are intermingled with each other. Therefore, it is difficult to assemble the device, and it is impossible to ensure a high dimensional accuracy for dimensions after assembling, such as the distance between the rotary transformers.
Furthermore, in the third prior art device, the two bearings 302 are held by the bearing-supporting projections 330 and 331 of the stationary cylinder 301, and the rotating shaft 303 is integral with the head moving unit 200a and the rotary cylinder 304 so as to be rotatably supported by the bearings 302. In order to suppress the runout of the shaft, therefore, the two bearings 302 must be separated from each other by a long distance, thereby requiring the thickness of the projection 330 of the stationary cylinder 301 in the side of the rotary cylinder 304, to be increased in the radial direction. The increased thickness of the projection 330 of the stationary cylinder 301 in the radial direction limits the space for the head moving unit 200a. As the whole size of the rotary magnetic head device 300 is reduced, the influence of this space limitation becomes larger. Therefore, it is difficult to secure a sufficient configuration space.
FIGS. 16 to 20 show a magnetic head device which is a fifth prior art device disclosed in, for example, Japanese Patent Application Laid-Open No. 60-209913 (1985). FIG. 16 is a perspective view of the magnetic head device, FIG. 17 is a front view of the device as viewed in the head gap direction in FIG. 16, FIG. 18 is an perspective view showing an operation state where a magnetic tape contacts with a rotary cylinder into which magnetic heads are mounted, and FIG. 19 is a section view of a rotary magnetic head device provided with the magnetic head device shown in FIG. 16. The rotary magnetic head device is used in a VTR or the like of the so-called segment recording type in which video signals of one field are recorded over a plurality of tracks.
In the figures, 501 designates magnetic heads, 502 is a head-attaching plate to which the magnetic heads 501 are attached, 502a is a reference plane of the head-attaching plate 502, 502b is an insertion hole through which a screw for attaching the head-attaching plate 502 to a rotary cylinder 504 is to be passed, and 503 is an adhesive for attaching the magnetic heads 501 to the head-attaching plate 502. The head-attaching plate 502 attached to the rotary cylinder 504 is supported so that it appears on the outer face of the rotary cylinder 504 through a window 505 formed on the rotary cylinder 504, and that the magnetic heads 501 slidingly contact with a magnetic tape 100 wound on the outer face of the rotary cylinder 504.
The reference numeral 507 designates tape guides, 508 designates air grooves formed on the rotary cylinder 504, 509 is a lead face for guiding the lower end of the magnetic tape 100, 510 is a stationary cylinder on which the lead face 509 is formed, 511 is a screw for adjusting the height of the magnetic heads 501, 512 is a flange to which the rotary cylinder 504 is attached, 513 is a rotating shaft which is integral with the flange 512, 514 designates bearings which rotatably support the rotating shaft 513 with respect to the stationary cylinder 510, and 515a and 515b are a stator and a rotor of a motor 400 for rotating the rotating shaft 513. The reference numeral 516 is a chassis to which the stationary cylinder 510 is attached, 517 is a screw for attaching the head-attaching plate 502 to the rotary cylinder 504, 518a and 518b are primary and secondary rotary transformers for sending and receiving signals, and 600 is a rotary magnetic head device consisting of these elements.
The operation of the thus configured fifth prior art device will be described.
The head-attaching plate 502 is generally made of an alloy such as brass, and is provided at the center portion with the insertion hole 502b through which the attaching screw passes. The upper face of the plate is made flat to function as the reference plane 502a. When the headattaching plate 502 is to be attached to the rotary cylinder 504, the plate is highly accurately positioned using the reference plane 502a with respect to the rotary cylinder 504, and then screwed thereto.
The magnetic heads 501 are fixedly adhered to the front end portion of the reference plane 502a of the headattaching plate 502, by the adhesive 503. More specifically, when the magnetic heads 501 are to be attached to the head-attaching plate 502, their attaching states are finely adjusted with respect to the adhesive 503 which has been just applied to the reference plane 502a and still remains uncured, and within the range of the adhesive 503. Each of the magnetic heads 501 is attached with a given head level difference Z1 and gap distance L1, and an adequate projection amount, head height and slant angle, and thereafter the adhesive 503 is cured, whereby the magnetic heads are fixed into the respective adequate attaching states.
As the adhesive 503, used is a resin adhesive having a low temporal dimensional change rate and a small coefficient of thermal expansion, such as an epoxy resin adhesive.
As shown in FIG. 19, the head-attaching plate 502 to which the magnetic heads 501 are stuck is attached to the rotary cylinder 504 by the screw 517, and the head height is adjusted by turning the screw 511.
FIG. 20 is a diagram showing the relationship between a head level difference error .DELTA.Z and the width TW of a track recorded on the tape. The relationship between the head level difference error .DELTA.Z and the track width TW in FIG. 20 is expressed as follows: EQU .DELTA.Z=1/2.times. TW1-TW2 (3)
When an error in the lead level difference is caused, therefore, the track width TW is affected by twice the degree of the error .DELTA.Z.
Recently, the track width is narrowed in order to attain a long-time recording. Under such a situation, in the view point of obtaining a stable reproduction signal, the suppression of the track width error , TW1-TW2 is an, important matter. As described above, it is important to suppress the head level difference error.
In the fifth prior art device having the configuration described above, among the values such as the gap distance between two adjacent magnetic heads 501, the projection amount of a head from the rotary cylinder, the level difference (the relative height Z1 between heads), and the relative azimuth angle, the gap distance L1 and the head projection amount can relatively accurately be adjusted. However, because the head level difference Z1 depends on the thickness of the adhesive 503, the accuracy of the adhering jig is limited, and the accuracy of the adhesive thickness itself is limited, there arises a problem in that it is difficult to accurately adjust the head level difference Z1.
Particularly, as described in conjunction with FIG. 20 and Equation 3, there is a problem in that the allowable head level difference error .DELTA.Z .lust be reduced as the track width TW becomes narrower.
In a case where the positioning technique of the fifth prior art device is applied to the third prior art device, the magnetic heads can follow a curved track as described above. However, in such a case, the level difference Z1 among the four magnetic heads 501 depends on the accuracy of the working step using the adhesive 503, and the accuracy of attaching the head moving device 200 to the rotary cylinder 504, and the track width error cannot be absorbed by the operation of the head moving device 200.
Furthermore, in a prior art device structured as described above, heat generated by heating elements accumulates in a space of the device. In the third prior art rotary magnetic head device, for example, the heating elements such as the coils 328 and 329 for vertically moving the magnetic heads 319 and 321 are located in the small space between the rotary cylinder 304 and the stationary cylinder 301, resulting in that the heat stays in this small space. When the rotary cylinder 304 has a small diameter in order to reduce the size of all apparatus, the heat value in the space is large and the heat radiation becomes insufficient. This may cause the coils to be overheated, resulting in that the electromagnetic properties cannot sufficiently be obtained, or that the coils are burned out.
In the third prior art device, for example, when signals recorded on the magnetic tape 100 are to be reproduced, driving currents of the level and polarity corresponding to an error signal which is included in reproduced signals obtained by the magnetic head A 319 and the magnetic head B 321 and which is proportional to the deviation from the recording locus on the magnetic tape 100 are supplied to the upper and lower coils 328 and 329. The magnetic head A 319 and the magnetic head B 321 are independently operated by controlling the currents supplied to the upper and lower coils 328 and 329, so that the deviation from the recording locus is eliminated.
When a given signal is to be recorded on the magnetic tape 100, however, the magnetic heads must be fixed in the moving direction. In the third prior art device, under a state where the upper and lower coils 328 and 329 are not energized by a current, the force of restraining the magnetic heads from moving in the vertical directions is weak. The magnetic head height cannot be highly accurately adjusted in the assembling process. Moreover, during a process in which a magnetic tape is actually running, the magnetic heads are easily displaced by an external force caused by the magnetic tape, thereby producing a problem in that the recording cannot be performed with accurately positioned tracks.
When the magnetic head A 319 and the magnetic head B 321 move vertically, the upper and lower plate springs 307 and 322 deform as shown in FIG. 21 in a manner different from the cantilever deformation which is observed when only one of the plate springs is deformed. This increases the rigidity of the upper and lower plate springs 307 and 322, so that large driving currents are required for obtaining a given displacement.
Furthermore, there is a problem in that, when the magnetic head A 319 and the magnetic thread B 321 move vertically, the amount of the projection of a head indicated by D in FIG. 21 is changed.